1. Technical Field
This invention generally relates to a process and a new nanotube growing mat on which nanotubes are grown in an organized and continuous manner and from where nanotubes, nanofibers, filaments, wires, cables and the like can also be produced.
2. Description of the Prior Art
There has been a great deal of scientific and commercial interest in carbon nanotubes in the last ten (10) years. Single Wall Carbon Nanotubes (SWCNT)and Multi-Wall Carbon Nanotubes (MW CNT) have what appear to be interesting commercial applications. The physical, electrical and optical properties of carbon nanotubes are in large part the reason for this interest.
Nanotubes can be produced by a variety of methods that include: laser ablation; electric-arc ablation; carbon vapour deposition and a reaction with a catalyst-carbon-paper.
In laser and electric-arc ablation graphite enriched with a metallic catalyst is evaporated, with the vapour produced condensed into nanotubes, these methods both require large amounts of energy. Carbon vapour deposition (CVD) by contrast requires approximately three (3) times less energy than either laser or electric-arc ablation.
In carbon vapour deposition the entire reactor is heated, yet CVD produces low yields and generates large quantities of amorphous carbon during pyrolysis.
Catalyst-carbon paper method uses a different approach, catalytic nanoparticles are deposited randomly on a random carbon substrate but only the carbon paper substrate is heated. US Patent Application 2003/0111334 A1 by Dodelet et al., teaches a method of carbon vapour deposition capable of producing carbon nanotubes in the absence of amorphous carbon at a low temperature. However, Dodelet et al, produce an intertwined mat of nanofibers. Similarly, in, “Growth of carbon nanotubes on Ohmically heated carbon paper” by Smiljanic et al, Chemical Physics Letters, 342(2001) pages 503-509, describes a method and apparatus for the production of nanotubes from a catalyst deposited on a porous carbon paper. Once again, the nanotubes or nanofibers produced are found in an entangled mat and difficult to separate. Furthermore, their production is intermittent and limited to about one minute of operation.
At present individual single or individual multi-wall nanotubes and nanofibers are produced in short strands varying from micrometer to millimeter lengths. Some production methods have little control of the nanotube length and the nature of the nanotubes, due in part to Van der Waals repulsive forces. Most frequently nanotubes are produced in an intertwined mat of short strands which are difficult to harvest. During any harvesting, there is a relatively large loss of nanotubes because of breakage and due to an inability to remove the nanotubes from the substrate on which they are produced.
The four methods of laser ablation; electric-arc ablation; carbon vapour deposition and catalyst-carbon paper reaction, are not meant to produce an ordered assembly of nanoparticles.